Imp Orb

Known to their creator, the long dead demon Lanf-taer, as 'Imp Orbs', each one holds a small demon of the imp variety, they have come to be dispersed throughout the world since his death in one of the demonic wars, centuries ago.

Lanf-taer distributed each of them to the heads of various groups of his cult, there were originally 25, but now there are only 14. His orders were to use them to aid in accomplishing his goals.

The imps were therefore originally summoned forth from the orbs in order to do mischief, or any other task, at the behest of the cult leader to which they were assigned. This allowed them a certain amount of time outside the orbs, which they enjoyed. In this time they also learnt a great deal about the world.

Since Lanf-taer's demise, the cults disbanded, and nobody thought further of the imps. Apart from the imps themselves, that is. The imps cannot tell anybody how to free them, as they simply do not know themselves. They are unaware of the world outside the orb unless the orb is held, and the summoning ritual did not require contact.

Each orb is a pocket dimension, which, when brought in contact with another orb, will merge with it. The imps therein will do combat, and one shall prevail. Eventually, the last imp standing hopes to have accumulated enough power through defeating the others and absorbing their life force to break free of their prison, by force alone.
When a battle has completed, one orb can be seen by the bearer to melt into the other, which retains exactly the same weight and size.

Whether this will work or not remains to be seen, but the imps generally do not wish to tell anyone of their plans.
Instead, the Imps who believe they will win these battles seek out other orbs, and those who do not seek to stay away. The imps are aware of the position of all other orbs, but only when held.

In order to be transported to other orbs, the Imps will lie to whoever finds them, promising them a great reward, should they manage to get the orb to all of the others. This is not likely to be the truth, but an Imp with access to the mind of its bearer can subtly manipulate their perception to make it seem like the truth. They will also use this ability to find the most likely lure that will interest the bearer.

Due to the survival instinct of the orbs that do not wish to be found by the others, they are often located in monster infested hellholes, which is their means of protection. If they are located by adventurers, they will attempt to guide them far away from the other orbs, and probably into an even more dangerous place where they will feel safer. Any place the adventurers survive is not safe enough.

Ironically, those who do wish to be found can also often be located in such places, dropped by their bearers as they were swarmed by monsters, while en route to or from another orb. The imps are patient enough to wait for more greedy adventurers, however. Even if they are somehow lost, they are confident that another orb will find them.

Plot hooks:
Perhaps the party, a greedy party, finds an orb that wishes to be found. It could trick them into seeking out the remaining orbs for them. Whether it rewards them, or stiffs them, afterwards remains to be seen.

Or perhaps they find an orb that doesn't wish to be found. The orb might offer them knowledge of the location of a powerful weapon, or somesuch, if they will only move it to another place. Whether the imp inside actually knows the location of said item is up for debate. It is doubtful that the party would be too pleased if they manage to get the imp to its destination, and it does not.

Or maybe they are on their way to getting an orb that doesn't wish to be found to its 'secure location' and they find themselves assaulted by another group of adventurers with another orb. Possibly this happens a couple of times. If they realise that all might not be as it seems, they may well be able to extort the imp with threats into actually helping them, instead of just saying it will.

Or maybe they find themselves with an orb that is hunting another orb carried by do-gooder adventurers who just want to help save an orb from whatever it told them was after it. What happens when you beat up the local heroes to get a talking rock off them? Can't imagine they didn't have a few friends.

Magical Properties:

Imp orbs are simply magical containers containing imps. Destroying an orb takes extreme force. Holding an orb allows mental conversation with the imp, and more, as the imp taps in to the bearers mind in order to trick them into helping. When held they are also aware of the location of all other orbs.